1. Field of the Invention
This invention relates to power splitters used with RF and microwave frequency signals in general and more particularly to a three way power splitter having a small package size that can be manufactured at low cost.
2. Description of the Related Art
Three way power splitters operating at frequencies below 1.5 GHz have been made with four ferrite core transformers along with appropriate resistors and capacitors arranged around the ferrite core transformers. These splitters provide multi-decade bandwidth. The power splitter components are typically packaged on a printed circuit board.
Referring to FIG. 1, a schematic diagram of a three way power splitter 20 is shown. Three way power splitter 20 has an input port 22 and three output ports 23, 24 and 25. An input matching transformer T1 is connected to input port 22. Output transformer T2 is connected to output port 23. Output transformer T3 is connected to output port 24. Output transformer T4 is connected to output port 25.
A capacitor C1 is connected between the transformers and ground. The series combination of resistor R1 and R3 is connected between output ports 23 and 25. Resistor R2 is connected between the junction of resistors R1 and R3 and output port 24. The input transformer T1 provides a 50 ohm impedance at the input. Capacitor C1 is required to match the reactive part of the impedance. The resistors R1, R2 and R3 provide isolation between the output ports 23, 24 and 25. Power splitter 20 is a 3 way power splitter since the input signal is split into three nearly equal output signals.
Referring to FIGS. 2–4, a prior art power splitter package 50 is shown. Power splitter package 50 has a printed circuit board 52 upon which are mounted a single core transformer 54 and two binocular core transformers 56 and 58. A chip capacitor 60 is soldered onto circuit board 52. Transformer 54 has several wires 61 wrapped around the core. A portion of wires 61 are twisted together to form a twisted pair 62. Transformer 56 has several wires 63 wrapped around the core. A portion of wires 63 are twisted together to form a twisted pair 64. Transformer 58 has several wires 65 wrapped around the core. A portion of wires 65 are twisted together to form a twisted pair 66.
Metal wrap around leads 68 are attached to the sides of printed circuit board 52 in order to make an electrical connection to the bottom side of circuit board 52. The transformer wires are welded to leads 68. The metal leads 68 would be soldered to an external printed circuit board (not shown) in an external electrical circuit. The three resistors R1, R2 and R3 would also have to be attached to printed circuit board 52.
Unfortunately, placing the capacitor next to the transformers takes up additional circuit board space and results in a larger overall package size. In addition, placing the capacitor complicates the assembly program followed by surface mount assembly equipment. This leads to lower production by the assembly machinery and higher cost. The use of the twisted pair wires results in a time consuming assembly process that is difficult to automate.
While power splitters have been used, they have suffered from being too large, difficult to assemble and expensive to produce. A current unmet need exists for a power splitter that takes up less printed circuit board space and that can be easily assembled.